ABSTRACT
PURPOSE: To compare the hemodynamic performance of three (Bottom Up non-ballet, Top-Down non-ballet, Top Down ballet) idealized stent graft configurations used during endovascular repair of abdominal aortic aneurysms, under the influence of various rheological models. METHODS: Ten rheological models are assumed and a commercial finite volume solver is employed for the simulation of blood flow under realistic boundary conditions. An appropriate mesh convergence study is performed and five hemodynamic variables are computed: the time average wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), endothelial cell activation potential (ECAP) and displacement force (DF) for all three configurations. RESULTS: The choice of blood flow model may affect results, but does not constitute a significant determinant on the overall performance of the assumed stent grafts. On the contrary, stent graft geometry has a major effect. Specifically, the Bottom Up non-ballet type is characterized by the least favorable performance presenting the lowest TAWSS and the highest OSI, RRT and ECAP values. On the other hand, the Top Down ballet type presents hemodynamic advantages yielding the highest TAWSS and lowest OSI, RRT and ECAP average values. Furthermore, the ballet type is characterized by the lowest DF, although differences observed are small and their clinical relevance uncertain. CONCLUSIONS: The effect of the assumed rheological model on the overall performance of the grafts is not significant. It is thus relatively safe to claim that it is the type of stent graft that determines its overall performance rather than the adopted blood flow model.
Subject(s)
Aortic Aneurysm, Abdominal , Hemodynamics , Stents , Humans , Hemodynamics/physiology , Aortic Aneurysm, Abdominal/surgery , Iliac Artery , Models, Cardiovascular , Stress, Mechanical , Aorta, Abdominal/surgery , Blood Flow Velocity , Blood Vessel ProsthesisABSTRACT
Hemodynamics in intracranial aneurysm strongly depends on the non-Newtonian blood behavior due to the large number of suspended cells and the ability of red blood cells to deform and aggregate. However, most numerical investigations on intracranial hemodynamics adopt the Newtonian hypothesis to model blood flow and predict aneurysm occlusion. The aim of this study was to analyze the effect of the blood rheological model on the hemodynamics of intracranial aneurysms in the presence or absence of endovascular treatment. A numerical investigation was performed under pulsatile flow conditions in a patient-specific aneurysm with and without the insertion of an appropriately reconstructed flow diverter stent (FDS). The numerical simulations were performed using Newtonian and non-Newtonian assumptions for blood rheology. In all cases, FDS placement reduced the intra-aneurysmal velocity and increased the relative residence time (RRT) on the aneurysmal wall, indicating progressive thrombus formation and aneurysm occlusion. However, the Newtonian model largely overestimated RRT values and consequent aneurysm healing with respect to the non-Newtonian models. Due to the non-Newtonian blood properties and the large discrepancy between Newtonian and non-Newtonian simulations, the Newtonian hypothesis should not be used in the study of the hemodynamics of intracranial aneurysm, especially in the presence of endovascular treatment.
ABSTRACT
The blood flow in the aortic arch and branch vessels in vitro is simulated,and the blood model is optimized with a non-Newtonian model.A numerical simulation analysis is conducted based on bidirectional fluid-solid coupling to analyze the hemodynamic characteristics(blood flow velocity,vascular wall pressure and vascular wall stress)in a cardiac cycle,and discuss their relationships with the formation of aortic dissection.It is concluded that the long-term existence of"chaotic"blood flow distribution in the blood vessel and the sudden changes of wall pressure and wall stress are liable to cause changes in the structure and function of the cells of the arterial wall,and ultimately induce the formation of aortic dissection.The study provides a more reliable basis for medical diagnosis,and further protects the life,health and safety of patients.